I used hydrogen peroxide since its so cheap. I filled up a cup with it, let a very smelly boar brush soak for about 5 minutes and presto, no smell at all. Its probably not great for the hair, but as long as its only done once I highly doubt that its going to be harmful. I am not completely sure why it worked as well as it did, but those of you with smelly boar brushes may want to give it a try. I was just desparate because my boar brush smelled so awful I couldnt even smell the scent of the cream I was using and it was either remove the scent or get rid of the brush.